Hydraulic fluid



April 9, 1946.

R. R. MCGREGOR ETAL 2,398,137

HYDRAULIC FLUID Filed June ll, 1943 4 Sheets-Sheet 1 san/029g Wray/ilary 1709105 k1/5:09901 inbenturs Qttutnep Apri 9, 1946' R. R. MCGREGOR ET AL 2,393,187

HYDRAULI C FLUID Filed June ll, 1945 4 Sheets-Sheet 2 April 9, 1946, R. R. McGRl-:GOR ETAL 2,393,187

HYDRAULIC FLUID Filed June 11, 1943 4 Sheets-Sheet 5 I OO' san/039g vase/gnu 709A vg lulsoas//f Www Qttutnry April 9, 1946 R. R. McGRl-:GOR ET AL 2,398,187

HYDRAULIC FLUID Filed June 11, 1943 4 Sheets-Sheet 4 Qtturncv Patented Apr. 9, 1946 HYDRAULIC FLUID Roh Roy McGregor, Verona, and Earl Leathen Warrick. Pittsburgh, la., assignors to Corning Glass Works, Corning, N; Y., a corporation of New York Application .time 1l., 1943, Serial No. 490,520

20 Claims.

This invention relates to compositions of matter and more particularly to nuids for use in hy draulic machinery for the transmission andabsorption of power, such as shock absorbers, brake mechanisms, artillery recoil mechanisms, lifting jacks. door checks, etc.

This invention is a continuation-impart of, our co-pending application Serial 'Number 432,530,

tiled February 26, 1942 now Patent No. 2,384,384

and assigned to the assignee of the present in vention.

Certain properties are required of iluids which are to be successfully 'employed as pressure transmitting or absorbing media. They must be stable both chemically and physically. They must not react with the materials of which the container or exposed parts are composed, that is, they must not cause corrosion of exposed metal parts or effect any substantial swelling of rubber parts. In addition, the viscosity of such fluids should remain within workable limits over a widge range of temperature and should notdisplay any tend ency to gasify or solidify under higher and lower temperatures respectively.

The primary object of this invention is to provide pressure transmission fluids which meet the above requirements and which are characterized by having a wide range of usefulness under extremely variable operation conditions.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in

which Fig. 1 is a viscosity-temperature chart of high polymeric dimethyl silicone fluids of different intrinsic viscosities as indicated;

Fig. 2 shows for purpose of comparison the viscosity-temperature slopes of a series of high grade hydraulic oils sold under the trade name of Univis; I

Fig. 3 is a viscosity-temperature chart of high polymeric liquid methyl silicones having a carbon to silicon ratio of 1.90 and different intrinsic viscosities as'indicated; and

Fig. 4 shows the viscosity-temperatures slopes of certain liquid silicones of our invention.

We have discovered that liquid organo-silicon oxide polymers possess properties which make them particularly suitable as hydraulic iluids per se or as constituents of fluid pressure media.- They are characterized by: relatively slight changes in viscosity over a wide range of temperature; low pour points; hlsh flash points; low volatility; low hygroscopicity; little or no corrosive or decomposing elect upon metal and rubber; and little or no gasication or solidication tendencies under the higher or lower temperature conditions enoounteredin the various types of hydraulic applications.' They'also show little or no tendency to be harmfully aiiected by v mechanical agitation.

Theliquid organo-silicon polymers with which our invention is concerned are compounds which contain organic radicals attached to silicon through a carbon atom and whose silicon atoms are joined to other silicon atoms by oxygen atoms, thus Si-O-Si. hydrolysis of hydrolyzableorganosilicanes and condensation of the hydrolysis products or by hydrolysis of a mixture of different hydrolyzable organo-silicanes and co-condensation of the hydrolysis products. By hydrolyzable organo-silieanes, we mean derivatives of SlHr having the general formula RvSiX(4.-y) where X is a hydrolyzable group as for example, halogen, amino, alkoxy, aroxy, acyloxy, y is 1, 2, or 3 and R is an organic radical joined through one of its carbon atoms to the silicon atom. Examples of such organic radicals are as follows: methyl, ethyl, -propyl, isoi propyl, butyl, amyl, hexyl, heptyl to octadecyl and higher; alicyclic radicals such as cyclopentyl, cyclohexyl, etc.; aryl and alkaryl radicals such as phenyl, monoand poly-alkyl phenyls as tolyl,

xylyl, mesityl, mono, di, and tri-ethyl phenyls,

mono, di, and tri-propyl phenyls, etc.; naphthyl, monoand poly-alkyl naphthyls as methyl naphthyl, diethyl naphthyls, tri-propyl naphthyl, etc.; tetrahydronaphthyl; anthracyl, etc.; aralkyl such as benzyl, phenylethyl, etc.; alkenyl such as methallyl, allyl, etc. The above organic radicals may also contain inorganic substituents such as halogens, etc.

Such organo-silicanes may be converted to the liquid organo-silicon oxide polymers by hydrolysis and condensation in the presence of an acid catt alyst as described in our co-pending application Serial Number 432,530 iiled February 26, 1942, now Patent No; 2,384,384 although other methods may be employed. Organo-silicon oxide polymers radical joined to' silicon through carbon, X the hydrolyzable radicals referred to above and 1l and y' are 1, 2, or 3. We prefer, in such copolymers, that the sum of y and il' be not less than 1.75. When y and/or 1l' is 3, simple ethers 30 of the type RaSiOSiRe result. In such others,

They may be prepared either by substituted, as, for example, R'RsSiOSiR.'Re or- RaSiOSiR/s.

The condensed hydrolysis products of silicanes or mixtures thereof and their polymerized products are now known as siloxanes (see page of Alfred Stocks book Hydrides or Boron and Silicon, published 1933). This invention, as shown above, is concerned with the organo-substituted siloxanes, that is, those siloxanes containing organic radicals attached to' silicon through carbon-silicon linkages.

We have found that for use as pressure transmitting or absorbing media those liquid organosiloxanes which are substantially completely condensed are to be preferred for most hydraulic applications since they are thermally most stable. However, even the partially condensed liquid organo-siloxanes may be useful forl certain applications where the temperature does not rise high enough to promote further condensation or polymerization. such as p-amino-phenol, mono-bennyl-p-aminophenol. a-nsphthol. -mphthol.. dlbenzyl-pamino-phenol. pyrogallol, diphenylamine, etc.,

polymerization of the unstable organo-siloxanes.

Although the above described liquid organosiloxanes are admirably ntted by themselves for hydraulic fluid purposes, we have found that they ties desired. When added to these liquids, or

ganic diluents may also be employed.

Furthermore, the use oi stabiliiiers has been found effective in preventing the further their low solidiiication temperature, their inertness Ato metals, rubber and other constructiai materials over the temperature range used, and theirhigh ilash point and low volatility.

-In the following table, a comparison of viscosity-temperature behavior of liquid high DOI!- meric dimethyl silicones with high grade hydraulic oils from petroleum base having equivalent viscosities at 100 F. is shown; viscosities aregiven in Saybolt Universal Seconds at temperature listed. Table v Dimm!!l m mmm sin 0 l 00116 1w bym In @wir i Y (univa a.

v u n "l ses Ik. I

2, (n) Il. M

In aircraft hydraulic fluids, this low rate of change oiviscosity with temperature is essential since fluid pressuredevices must operate smoothly afterstanding in cold climates or on changing suddenly from high altitudes where the tempera- -ture maygo as low as 'F to low altitudes where the temperature may be as high as +110 F. Under tropical night conditions, where high temperatures are accompanied by high humidities, 'the insolubility of the liquid 111811 As examples of representative'hydraulic nuids of this invention, we have found that the following liquid organo-siloxanea have highly desirable characteristics.

Examens 1 A Polymeric liquid dimethyl silieones resulting from the hydrolysis of dimethyldiethoxysilicane as described in my eopending application, Serial Number 432,530 led February 26, 1m, now Patent No. 2,384,384, are freed from lower polymeric materials by distilling under 10 mm. pressure with CO: blowing through until the temperature of the residual liquid in the still reaches 250' C.

inglntrinsicviscositymaybeobtalnedtosulithe individual application of hydraulic iluid, as shown in Fig. l. All liquid dimethyl silicones prepared by hydrolysis of substantially pure Y (CH3) aSMOEIDa have the same melting temperature, namely, about -40 C. although they may be supercooled as low as C. without solidifying.

The principal characteristics which adapt these high polymeric liquid dimethyl silicones to use inaircraithydraulic iluidsaretheirlow rate of changeofviscositywithchangeoftemperature,

organo-siloxanes in water and their ability to psevent access of water to surfaces with which they have been in contact is importat, since prevention ofjiccess oi moisture avoids clogging the apparatus by freezing out at high altitudes.

iiqmdsiesumng from the @hydrolysis or somele equivalents or (cinnamon). ma 1o male eqmvaients .ot (cmmuortnue distilled u pottemperauueof250C.underl0mm.tol-e move low. polymers as described in kampte 1; Buch liquids have approximately the exmlrioal where y=1.9. As in me pure dimethyl siliconen' ofExample1,theymayalsobeprodueedina range of intrinsic viscosities as shown bythevis-V cosity-temperature curves of several such polymersinFlg.3. 'I'heintrinsicviscositiesofthese liquid mono-methyl-dimethyl siloxane copolymers are, in general, lower than those obtainableY from dimethyl silicone polymers, and their other properties are quite similar. However, they. posseas even lower freezing points and melt at C.

A comparison of the viscosity ci high Polym- 'eric liquid siloxanes having a ratio of 1.9 methyl groups persilicon with the viscosity cfa high grade hydraulic oil from a petroleumbase is given in the following table.

Exams: 3

Liquid copolymers resulting from the hydrolysis oi a mixture of 3 mole equivalents of (CPB) :81(OEt) Table III Methyl siloxane Ptuule Temp., F. iluildse A, Imm 54) (sec iig. 2)

92 51. 5 220 m 750 000 l, 050 19, m0 l, wo 65, (XX) ExAMPu.' 4

In a manner entirely similar to Example 1 of this application and as described in our pending application Serial Number 432,530 filed February 26, 1942, now Patent No. 2,384,384 diethyl dil ethoxy silicane was hydrolyzed and converted to a high polymeric hydraulic uid. This material is also characterized by a low rate o1 change of viscosity with temperature and the inertness ci the materials of the preceeding examples. A comparison of the viscosity of the high polymeric silicone with the viscosity of a high grade hydraulic oil from a petroleum base is given in the following table where the viscosities are in l Saybolt Universal seconds.

Table IV Petroleum base Diethgl silicone h draullc oil Temp., F. (see Fig. 4) Univls 48) (ses Fig. 2)

EXAMPLE 5 A liquid copolymeric siloxane containing l0 mole per cent of the structural unit has a solidication temperaturev of -55 C. and a temperature-viscosity slope of 1410 from 0 C. to 100 C. (the slope being the value of the quotient A log N A log l/T where N is viscosity and T the absolute temperature) as contrasted with a solidiiication temperature ot -19 C. and atemperature-viscosity slope o1 over 42000 tor Gull Pride 40, a standard hydraulic iluid. 'Ihe viscosity of this siloxane at 0 C. was 350 centistokes. Its chemical properties are similar to those of the methyl Asiloxanes discussed above.

muri.: 6

A liquid copolvmeric siloxane containing 10 mole percent of the structural unit (olmo-#si-o Y (C n) and mole per cent of the structural unit (ermelo has a solidication temperature of 45 C. and a temperature-viscosity slope of 1300 trom 0 C. to C. At 0 C. this siloxane had a viscosity of 285 centistokes. Its chemical properties correspond with those of the methyl siloxanes. A comparison oi the viscosity of the copolymers described in Examples 5 and 6 with that of a Detroleum base hydraulic oil is given in the table below where viscosities are in Saybolt Universal seconds.

Table V Petroleum Temp PhIIEoSio-Mzsiig AmllBlo-Merlgsitz hy-il C0 X. 00 Bl X. F (netfirms (Kaman (U'iivio) (sec Fig. 2)

21o. s so oz 10o am aco 26o o 4,600 3.400 1,500 -22 n.000 1.000 sooo Exmrtn 'I The siloxane [(CsHsNCIzSilnO known as bis-phenyl-dimethylsilicyl oxide is a liquid having a solidiilcation temperature o1' -76 C. and a temperature-viscosity slope of 1280 from 0 C. to 100 C. Like most of the completely organosubstitnted dlsiloxanes it is highly resistant to further polymerization. In general, siloxanes of this type (i. e. the completely substituted disiloxaries) possess properties which especially adapt them for use as hydraulic uids.

The liquid organo-siloxanes of our invention are eminently adapted to be used as pressure transmitting or absorbing media, in hydraulic machinery and similar mechanism which depend for their successful operation on the constancy of resistance to flow through small orices oered by a viscous liquid under various conditions. One of the outstanding advantages of the liquid organo-siloxanes as hydraulic media is the wide variation in viscosity attainable in a given composition by controlling the extent of polymerization so that a given organo-siloxane may be used in a variety of hydraulic applications requiring liquids of diil'erent viscosities. In this regard. liquid organo-siloxanes have been prepared ranging in viscosity from 11,4 centistokes up to over 100,000 centistokes. Examples of the var ious types of hydraulic applications for which these organo-siloxanes are iltted are hydraulic pressure actuating mechanisms, hydraulic clutches. shock absorbers, dash pots, vibration dampeners, artillery recoil mechanisms, lifting Jacks, door checks, etc., i. e. in general, hydraulic apparatus wherein a liquid is utilized to eiect relative movement o a member such as a piston and an enclosinz chamber.

We claim: A 1. In the process of eiiecting movement of a movable member within an enclosing chamber, the step which consists in transmitting pressure to said movable member through a. homogeneous liquid medium, the maior constituent ofwhich is,

a liquid organo-siloxane whose organic substituents consist essentially of organic radicals attached to silicon through carbon-silicon linkages,

at least some of said organic radicals being alkyl lo,

radicals containing less than three carbon atoms. 2. In the process oi eil'ecting movement of a movable member within an enclosing chamber,

the stepwhich consists in transmitting pressure to said movable member through a homogeneous liquid medium, the maior constituent of which is a liquid organo-siloxane whosev organicsubstit-- uents consist essentially of organic radicals at` to said movable member through a liquid medium' consisting essentially of `a substantially completely condensed liquid organo-siloxane whose organic substituents consist essentially oi monovalent hydrocarbon radicals attached to silicon through carbon-silicon linkages, at least some of said hydrocarbon radicals being alkyl radicals containing less than three carbon atoms.

4. The process according to claim 3 wherein the liquid organo-siloxane is completely conf densed and wherein the hydrocarbon radicals are principally alkyl radicals having less than three' carbon atoms.

5. 'I'he process according to claim 3 wherein the hydrocarbon radicals consist of alkyl radicals having less than three carbon atoms and aryl radicals. Y

6. The process according to claim 3 wherein the hydrocarbon radicals consist of alkyl radicals having less than three carbon atoms and phenyl radicals.

7. The process according to'claim 3 wherein the hydrocarbon radicals consist of alkyl radicals having less than three carbon atoms.

8. The process according to claim 3 wherein the hydrocarbon radicals consist of methyl radicals.

9. The process according to claim 3 wherein the liquid organo-siloxane is liquid dimethyl silicone.

10. The process according to claim 3 where the liquid organo-siloxane is liquid dimethyl silicone which is substantially non-volatile below 250 C. at 10 mm. pressure and which has a free point below 40 C. v

11. 'I'he process according to claim 3 wherein the liquid organo-siloxane is liquid diethyl silicone.

12. The process according to claim 3 wherein the liquid organo-siloxane is bis-phenyldimethylsilicyl oxide. l

13. Hydraulic apparatus comprising. in combi.' nation. a movable member and a liquid medium arranged in contact with said member, said liquid medium consisting or a liquid organo-siloxane whose organic substituents .consist essentially oi monovalent hydrocarbon radicals attached to lilicon through carbon-silicon linkages, at least some of said hydrocarbon radicals being-alkyl radicals having less than three carbon atoms.

14. Hydraulic apparatus comprising, in combination, a movable member and a liquid medium arranged in contact with said member, said liquid medium consisting oi' a 'substantially completely condensed liquid organo-siloxane whose organic substituents consist essentially of monovalent hydrocarbon radicals attached to silicon through carbon-silicon linkages. at least some oi' said hydrocarbon radicals being alkyl' radicals having4 less than three carbon atoms.

l5. Hydraulic-apparatus comprising, incombination, a movable member and a liquid medium arranged in contact with said member?, said medium consisting of a substantially completely condensed liquid organo-siloxane whose 'organic .substituents consist essentially of alkylradicaia having less than three carbon atoms andfphenyl radicals attached to silicon through carbon-'lilicon linkages.

16. Hydraulic apparatus comprising; in` combination, a movable member and a liquid medium' arranged in contact with' said member,said liquid medium consisting of a substantially completely' condensed-liquid organo-siloxane whose orl'lnic substituents consist essentially of alkylradicals attached to silicon through carbon-silicon linkages; said alkyl radicals having less carbon atoms. `1"T. Hydraulic apparatus comprising, in combi..- nation, a movable member and a liquid medium arranged in contact with said member, said liquid mediu'mconsistingof a liquid dimethyl 18. Hydraulic apparatus comprising, in combi.' ation, a movable member and a liquid medium arranged in contact with said member. said liquid medium consisting ci a liquid dimethyl silicone which is substantially non-volatile below 250 C. at 10 mm. pressure and which has a freezing point below v-40 C.

19. Hydraulic apparatuscomprising, in combination, a movable member and a liquid medium arranged in contact with said member, said liquid medium consisting of a liquid dlethyl silicone.

20. Hydraulic apparatus comprising, in combination, a movable member vand a liquid medium arranged in contact with said member, Said liquid medium consisting of bis-phenyldimethylsilicyl oxide.

- ROB ROY MCGREGOR.

EARL LEATHEN WARRICK. 

